Copyright Goodheart-Willcox Co., Inc. 827 Chapter 24 ∣ Track Steering Systems The hydraulic steering motor drives the sun gear short shaft that in turn drives the right sun gear. The sun gear short shaft also drives the sun gear long shaft, which acts like a reverse idler causing the sun gear long shaft to reverse the direction of the left sun gear. The design of the sun gear short shaft meshing with the sun gear long shaft results in the hydraulic steering motor driving the right sun gear in one direction and the left sun gear in the opposite direction, causing the tractor to steer. When the hydraulic steering motor reverses its direction of rotation, the tractor steers in the opposite direction. When the tractor is driving forward or in reverse along a straight path, the hydraulic steering motor holds the two sun gears stationary, which causes the planetary carriers to drive both tracks forward or backward at the same speed. When the hydraulic steer- ing motor is the only input into the steering differential, one sun gear is driven clockwise and the other sun gear is driven counterclockwise, causing the tractor to counter rotate. The direction of counter rotation is determined by the direction of the hydraulic steering motor’s rotation. When both the transmission and the hydraulic steering motor are deliv- ering power into the steering differential, the tractor moves and steers simultaneously. John Deere Twin Rubber Track Differential Steering John Deere manufactures twin rubber track tractors in their two largest agricultural horsepower applications, the 8RT and 9RT tractors. The twin rubber track tractors are equipped with differential steering, Figure 24-20. The steering differential receives input from the transmission via the powershift transmission output shaft and a drive gear and driven gear. The driven gear propels the bevel pinion gear, which propels the bevel ring gear. The bevel ring gear drives the bevel gear shaft, which drives the two planetary carriers. If the machine is propelled in forward or reverse along a straight path, the planetary carriers drive the two ring gears in the same direction (either forward or reverse). The hydraulic steering motor is linked to the two planetary sun gears, which are held stationary by the hydraulic steering motor while the tractor is moving on a straight path in forward or reverse. When the operator steers the tractor, the hydraulic steering motor drives one plan- etary sun gear clockwise and the other sun gear counterclockwise. For example, if the Input into right final drive’s sun gear Ring gear Sun gear Powershift transmission output shaft Hydraulic steering motor Driven gear Drive gear Planetary carrier Bevel ring gear Reverse idler Steering cross shaft Input into left final drive’s sun gear Bevel gear shaft Cluster gear Ring gear Planetary carrier Sun gear Goodheart-Willcox Publisher Figure 24-20. Deere twin rubber track tractors use differential steering. The transmission is responsible for driving the planetary carriers. The hydraulic steering motor is responsible for holding or driving the planetary sun gears via the large external-tooth ring gears. The planetary ring gears (internal-tooth ring gears) are the outputs that drive the input to the final drives.